I have an ASROCK A75 Pro4 motherboard with the latest BIOS version P.2.50.

I used to have 2 Corsair 2GB RAM modules, and they worked just fine in slot 0 & slot 2 (total 4GB RAM).

I recently installed an extra 2GB RAM module with similar specs but different brand.

There are 4 DIMM slots on the board, and my original 2 RAM sticks were always in slot 0 and slot 2. I'm not a hardware expert, but I noticed that when I insert my new RAM stick in slot 1 (slot 3 is empty), BIOS reports "Single-Channel Memory Mode". However, if I move it to slot 3 (leaving slot 1 empty), BIOS reports "Dual-Channel Memory Mode". Why is that?

In any case, no matter where I insert my new RAM, the BIOS reports 3 x 2GB for a total of 6GB.
However, no matter which OS I boot (tried the latest Gentoo live minimal image and other Linux flavors) I can only see 4GB (top, free, etc.).

This motherboard provides four 240-pin DDR3 (Double Data Rate 3) DIMM
slots, and supports Dual Channel Memory Technology. For dual channel con-
guration, you always need to install identical (the same brand, speed, size
and chip-type) DDR3 DIMM pair in the slots of the same color. In other words,
you have to install identical DDR3 DIMM pair in Dual Channel A (DDR3_
A1 and DDR3_B1; Blue slots; see p.12 No.7) or identical DDR3 DIMM pair in
Dual Channel B (DDR3_A2 and DDR3_B2; White slots; see p.12 No.8), so
that Dual Channel Memory Technology can be activated. This motherboard
also allows you to install four DDR3 DIMMs for dual channel con guration, and
please install identical DDR3 DIMMs in all four slots

So afaik you need to install 2 extra modules. If you follow the manual they should be identical to the installed ones.

As far as the OS memory report are they 64 bit OS's or 32 bit, if 32 then they will only report 4gb.

I haven't looked at the manual for the MB, but typically if you put an odd amount of memory 1,3, etc, then you don't get dual channel memory.
Some MB's have a setting in the bios to switch from dual to single, an odd amount HAS to run in single (if you think about it, it's obvious)_________________Asus m5a99fx, FX 8320 - nouveau & radeon, oss4
Acer laptop E5-575, i3-7100u - i965, alsa
---both---
4.14.62 kernel, profile 17.0 (no-pie) amd64-no-multilib
gcc 7.3.0, eudev, openrc, openbox, palemoon

2) that 3.7gig reported by the kernel is scarily close to what is visible on a 32bit system once the kernel has reserved ~250meg for itself

could you please paste the output of uname -a _________________The best argument against democracy is a five-minute conversation with the average voter
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if you have memory slots 1 2 3 4
1 and 3 are dual channel, 2 and 4 are dual channel.

you can put memory in 1 2 and 3 but you'll only have single channel with an OS potentially seeing max of 6 gb.
you can put memory in 1 3 and 4 again only single channel, the bios will report 6 because it sees it, but an OS isn't likely to see channel 4 thus reporting only 4 gb.

Please note that my VGA is onboard, so part of the RAM will also be shared with the video display.
I guess that's also why /proc/meminfo doesn't show me the full 4GB.

In any case, I understand that Dual-Channel requires a 2x2 setup (although I didn't know it had to be exactly the same brand -- you will notice from the dmidecode output that the RAM sticks have identical specs, or at least it seems so even on the manufacturer's tech sheet).

However, what's with Single-Channel memory mode as mentioned in my first post?
When I have the following configuration:

So in this case, even if I can't benefit from dual-channel technology, shouldn't the 64-bit OS be able to see the full 6GB?

BTW, I have no idea what DDR3-{SD,SS,DS} mean, but it seems to me that the 3 sticks are pretty much the same. [EDIT: I just searched on the net and found out it's just the way they are physically built, ie., chips on one side only, on both sides, etc. -- not a big issue]

If I were to buy another Kingston KVR1333D3N9/2G and place it into Slot 3, would my issue be solved?

The manufacturer will test memory configurations that they list in the book. Other configurations may work but there is no guarantee.

You can, if the board supports it, put a single stick in, but putting 2 in one bank and 1 in the next is an oddball case that almost no motherboard manufacturer will actually test, especially if one module is not identical to the others.

I have mixed brands before, but in almost every case if all sticks aren't the same exact size (of RAM) then something unfortunate will usually happen. Like it decides all the sticks are the size of the smallest, if you're lucky, or maybe that it shouldn't boot all, or only recognizes the first stick.

I've had a motherboard that work with two different module sizes, but each bank must have identical modules in that bank (0 and 2, 1 and 3) and the lowest-numbered bank is supposed to have the biggest sticks if I remember right. I think that board was an Asus. I remember playing around with that one having found some dimms for cheap online, and didn't get happy results.

I've also mixed timings before, but again identical timings in the same-color slots. The board may decide all the timings are the same as the worst modules.

So in this case, even if I can't benefit from dual-channel technology, shouldn't the 64-bit OS be able to see the full 6GB?

BTW, I have no idea what DDR3-{SD,SS,DS} mean, but it seems to me that the 3 sticks are pretty much the same. [EDIT: I just searched on the net and found out it's just the way they are physically built, ie., chips on one side only, on both sides, etc. -- not a big issue]

Single-Sided, Double-Sided RAM ... Not sure where you got SS from_________________The best argument against democracy is a five-minute conversation with the average voter
Great Britain is a republic, with a hereditary president, while the United States is a monarchy with an elective king

Last edited by Naib on Wed Oct 17, 2018 9:07 pm; edited 2 times in total

Again, I haven't read the MB manual, but if you have 0,1 and 2 populated then you will ONLY get single channel
If the bios allows you to set memory as dual or single and you have 3 sticks then it will probably ignore the 3rd stick when offering it to an OS, if it's set to dual.

And it could be that it simply won't offer the 3rd stick as usable if only 3 are available.

A lot of what I'm conjecturing depends on how the bios is written. And it's been years since I've used an asrock board.

As far as adding another stick to match the odd one, it should work.
They don't have to be the same manufacturer (though it's recommended and they probably only test for that) but if the specs are the same it should work._________________Asus m5a99fx, FX 8320 - nouveau & radeon, oss4
Acer laptop E5-575, i3-7100u - i965, alsa
---both---
4.14.62 kernel, profile 17.0 (no-pie) amd64-no-multilib
gcc 7.3.0, eudev, openrc, openbox, palemoon

If the bios allows you to set memory as dual or single and you have 3 sticks then it will probably ignore the 3rd stick when offering it to an OS, if it's set to dual.

And it could be that it simply won't offer the 3rd stick as usable if only 3 are available.

A lot of what I'm conjecturing depends on how the bios is written. And it's been years since I've used an asrock board.

As far as adding another stick to match the odd one, it should work.
They don't have to be the same manufacturer (though it's recommended and they probably only test for that) but if the specs are the same it should work.

Thanks, it all sounds crystal clear. I guess I just can't fully trust what the BIOS screen says. In other words, if the BIOS reports Single-Channel with all 3 sticks detected for a total of 6GB then it's also possible that it may not "offer" one of the three to the OS when it boots, making the memtotal in a 64-bit Linux at 4GB in my case.

Naib wrote:

Any reason posting here and not ubuntu forum

As stated earlier, I was using the Gentoo live minimal installation CD to... install Gentoo on this particular PC which is currently running Ubuntu.
I ran "uname" there so I could easily post it here instead of using a console-only Gentoo live system.

You are trying to mix RAM with different 'geometries'. That may or may not work. It depends how tolerant the memory controller is.

RAM is divided into 'rows' and 'columns'. Your single sided stick has only half, or a quarter the number of RAM chips on it compared to the double sided sticks.
As the two sorts are both 2GB, The single sided stick requires one or two extra address bits per chip over your double sided sticks.

Some DRAM controllers will work, some won't as they expect all the the DRAM to have the same number of rows and columns._________________Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
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